In recent years, in order to cope with the air pollution and the global warming, it is sincerely desired that the emission amount of carbon dioxide be reduced. In the automobile industry, expectations are centered on such reduction of the emission amount of carbon dioxide by introduction of the electric vehicle (EV) and the hybrid electric vehicle (HEV). Therefore, development of an electric device such as a secondary battery for driving a motor, the electric device serving as a key for practical use of these vehicles, is assiduously pursued.
As the secondary battery for driving a motor, a lithium ion secondary battery having high theoretical energy attracts attention, and at present, development thereof rapidly progresses. In general, the lithium ion secondary battery has a configuration in which a positive electrode, a negative electrode and an electrolyte located therebetween are housed in a battery casing. Note that the positive electrode is formed by coating a surface of a current collector with positive electrode slurry containing a positive electrode active material, and the negative electrode is formed by coating a surface of a negative electrode current collector with negative electrode slurry containing a negative electrode active material.
In order to enhance capacity characteristics, output characteristics and the like of the lithium ion secondary battery, selection of the respective materials is extremely important.
Heretofore, a non-aqueous electrolyte secondary battery has been proposed, which has a hexagonal layered rock salt structure belonging to the space group R-3m, and contains Li in the 3b site in which transition metal is contained (for example, refer to Japanese Patent Unexamined Publication No. 2007-242581). This lithium-nickel-manganese composite oxide is represented by a formula Li[LixNiyMnz]O2−a. Then, in the formula, x ranges: 0<x<0.4; y ranges: 0.12<y<0.5; z ranges: 0.3<z<0.62; and a ranges: 0≦a<0.5, which satisfy the following relationships: x>(1−2y)/3; ¼≦y/z≦1.0; and x+y+z=1.0.
Moreover, heretofore, a cathode composition for a lithium ion battery has been proposed, which has a formula (a) LiyM1(1−b)Mnb]O2 or a formula (b) Lix[M1(1−b)Mnb]O1.5+c (for example, refer to Japanese Patent Unexamined Publication No. 2004-538610). Note that, in the formulae, the following relationships are satisfied, which are: 0≦y<1; 0<b<1; and 0<c<0.5, and M1 denotes one or more types of metal elements. However, in the case of the formula (a), M1 is metal elements other than chromium. Then, this composition has a single-phase form having an O3 crystal structure that does not cause phase transition to the spinel structure when a cycle operation of a predetermined complete charge/discharge cycle is performed.